Social cost of carbon under shared socioeconomic pathways

The Social Carbon Cost (SCC) measures present value of future economic damages caused by an additional ton of carbon emissions, and is widely used by governments to design climate policies. Although the use of SCC is very extensive, its predictions are very difficult. Because the SCC is defined by social welfare associated with economic growth and population, its estimation is necessarily dependent on future assumptions that are difficult to project. Many approaches consider the impact of population or economic growth on the SCC, but these socioeconomic factors must be grounded on solid assumptions concerning political, technological and environmental developments. Over the past seven years, the climate change research community has established five plausible socioeconomic narratives, called 'shared Socioeconomic Pathways’ (SSPs), numbered SSP1–SSP5. These scenarios provide descriptions of how the future might unfold in several key areas. To this end, we use the Dynamic Integrated model of Climate and the Economy (DICE) to update the SCC under the five socioeconomic pathways, while also considering alternative damage functions and the social welfare discount rate to address uncertainty. The result of the China Climate Change integrated assessment model (C³IAM) were used to re-estimate parameters in DICE, therefore characterize the SSPs. The results show that, in a world developing towards regional rivalry (SSP3), the SCC today will likely double compared with other scenarios. If emerged developing countries will follow the same path as previous industrializations (SSP5), the SCC will experience a rapid increase after 2060. Inequality (SSP4) will experience low mitigation pressure under a sustainable development scenario (SSP1), while the historical development pattern (SSP2) will have a moderate SCC with higher uncertainty. The results can provide carbon price benchmarks for policy makers who hold different attitudes towards the future and can help address the need to avoid regional rivalries and fossil-fueled development, which may counteract mitigation efforts.